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+--- Thread: uncoupled rear brake mods (/showthread.php?tid=9631)
RE: uncoupled rear brake mods - Tony Press - 17-10-2024
Back in the 50s I devised an extended cotter for the front brake levers with a tension spring up to the backplate to assist.
They are still on the chummy.
Somewhere I have details if wanted,
Cheers.
RE: uncoupled rear brake mods - squeak - 17-10-2024
Back in the early sixties I copied your idea Tony and the extended cotters are also still on the car. The U shaped shims are in use and the oversize pivot pin was achieved by wrapping it in a strip of steel.
RE: uncoupled rear brake mods - Dave Mann - 18-10-2024
I should have added that I converted my first Seven back to cable brakes as I thought that the supply of hydraulic spares would dry up before cable spares. This proved to be so when I still have one hydraulic braked Seven and I fitted a pattern master cylinder which worked OK over about 50 miles until I was parking when I found I had no foot brake fortunately the reflex grab the handbrake saved the day. That master cylinder was binned and replaced with a Lockheed 13/16" one.
RE: uncoupled rear brake mods - `Gordonhbm - 18-10-2024
Dave, thanks for your input yesterday. I found this really helpful and caused me to to have flash of understanding! What this was saying to me is that a wear free system will have the ball ends on the cam levers correctly under the kingpins and on the kingpin axis. So with the brake shoes correctly set up with shims so that the cam face is in full contact, ie parallel to the end faces of the shoes, the pivot pin of correct diameter, then a brake lining of suitable thickness will be in near contact with the drum at both ends of the shoes. This then is the optimum set up, preventing the inner wheel from being braked on full lock, and can be kept in this state by adjusting the shims at both ends of the shoes to take up wear of the linings. The brake cable is not used to adjust brake shoe clearance - its length being set to minimise cable sag without affecting shoe clearance.
However because the pivot pin is fixed the shoes are not self centralising within the drum so unequal wear will occur along the length of the shoe. This can be overcome in principle by mounting the pivot pin in a separate block on the back of the backplate with the hole in the backplate being 1/8" larger in diameter and the fixing holes on the block also being larger by the same amount compared to its two fixing studs in the back plate. The block is held by the nuts, being fitted with Thackery washers so that the assembly is just free to move under load. When the brakes are applied heavily whilst stationary this will cause the brake shoes to be centralised. I had this system on one of my cars and it worked well for me. You could make the bearing surface of the pivot pin tapered and the shoe ends tapered to match so by screwing in the taper the end of the shoe could be adjusted to take up play.
If the sag of the front cable is a problem then by using a pivoting balance bar with two rods in place of the cable would work and the compensation would likely be improved due to lower friction.
RE: uncoupled rear brake mods - Dave Mann - 15-11-2024
During a service of one of our cars I found the FOS brake was binding on lock and removed the front brake cable aluminium swivel and found whilst it had a nice large radius in the middle the ends have a sharp radius and the cable had dug into them preventing the cable from sliding. As a temporary fix i dressed the damage out whilst I made a 3" diameter pulley to replace the aluminium swivel.
I mentioned this to two friends and they both said that they both use a pulley in place of the aluminium swivel.